Prediction of the remaining reserve time of a discharging battery is very desirable information in situations where a critical process is dependent upon the battery capacity. Such a prediction may require the monitoring of a condition of a battery and an extrapolation therefrom to determine the life of the battery in which it may be depended upon to power the critical process.
There are many approaches to battery capacity prediction. In one approach (U.S. Pat. No. 4,952,862) reserve time is predicted based on the measured discharge characteristics of a battery. The discharge is characterized by a discharge curve with a linear and exponential region and by a measured plateau voltage. These characterizations combined with a real time monitoring of dynamic parameter of the battery allows a running prediction of remaining battery reserve time with continuously improving accuracy. This system however is highly dependent upon an ideal discharge profile and many batteries diverge significantly from this ideal profile.
In another approach (U.S. Pat. No. 4,876,513) the battery voltage is compensated for resistive voltage drop and continuously compared with the allowable end voltage to provide a compensated voltage level from which the remaining battery capacity is calculated. The approach is also highly dependent upon the ideal discharge profile of the battery.